We have recently discovered that substitution of 2 fluorine atoms at C-10 of prostacyclin not only achieves the expected stabilization of the molecule to acid hydrolysis, but also serves to maintain, qualitatively and quantitatively, the biological spectrum of natural prostacyclin. Based on this discovery it is our objective to synthesize prostacyclins in which hydrogens adjacent to the labile enol ether grouping are replaced by fluorine e.g., at positions 4,4; 5; and 7,7. By multiple difluorination it should then be possible to obtain even more acid stable prostacyclins. The resulting intermediates could serve as points of departure by chemists in industry for compounds possessing therapeutically useful properties. The same "difluoro principle" will be applied to the synthesis of difluorothromboxane in which the two fluorine atoms are adjacent to the very readily hydrolyzed bicyclic acetal grouping. The synthesis of such a compound would be of great interest since it is practically impossible to synthesize the natural substance which possesses a half life of 30 seconds. Difluorinated arachidonic acids in which select methylene groups contiguous to the four double bonds are replaced by CF2 will be synthesized. These substances will be employed as substrates for the cyclooxygenase as well as the subsequent enzymes of the arachidonic acid cascade. Depending on the location of the CF2 grouping one would expect either formation of the corresponding difluoro prostaglandins or observe inhibition of the respective enzyme(s). Inhibitors of this type may possess high selectivity for the cyclooxygenase and/or lipoxygenase pathways.